class Circle:
    def __init__(self,r):
        self.r=r

    def calculate_are(self):
        return pow(self.r,2)*3.14

    def calculate_perimeter(self):
        return self.r*2*3.14

r=eval(input("请输入圆的半径: "))
c=Circle(r)
print(f"圆的周长为{c.calculate_perimeter()}")